Humification is a process whereby the carbon of organic residues is transformed and converted to humic substances through biochemical and abiotic processes. Degradation of PFOS by laccase-induced enzyme catalyzed oxidative humification reactions (ECOHRs) was studied using 1-hydroxybenzotriazole as a mediator. Approximately 59% PFOS was transformed in a mineral buffer over 162-day incubation with the initial PFOS concentration at 1.0 uM. Degradation followed pseudo-first order kinetics with a reaction rate constant of 0.0043/d (r2 = 0.86), which was similar to that measured for PFOA degradation (0.0044/day, r2 =0.89). High-resolution mass spectrometry analysis showed that ECOHRs transformed PFOS to partially fluorinated compounds. These products could be generated through the dissociation of SO3- group to produce perfluoroalkyl radicals, followed by radical rearrangement and coupling with other co-existed non-fluorinated radicals. This finding suggests that ECOHRs may have a great potential for removing PFOS from a contaminated environment.